1. Field of the Invention
This invention relates to exploding-bridgewires. More particularly, this invention relates to an exploding-bridgewire and an exploding-bridgewire firing set to reliably initiate any explosive. Still more particularly, but without limitation thereto, this invention relates to use of exploding-bridgewire driven multiple flyers to impact and initiate the explosive.
2. Description of the Prior Art
For safety reasons, high voltage exploding-bridgewire detonators are used in ordnance applications. These detonators utilize the heat, shock and energy from an exploding-bridgewire to initiate the surrounding explosive pressed to a closely controlled density at the bridgewire/powder interface. However, use of an exploding-bridgewire to initiate an explosive has been limited to explosives no more insensitive than pentaerythrite tetranitrate (PETN).
Recently, a need has arisen for a more stable, more reliable and a higher temperature explosive than PETN. The major effort has been in the use of the explosive hexanitrostilbene (HNS). To date, the only reliable method of initiating HNS is by an exploding foil concept.
The conventional exploding foil concept of initiating insensitive explosives has been based on dumping sufficient electrical current within a short period of time (burst current) to explode a small and thin metal bridge. The resulting electrically exploded metallic vapor of this flat metal foil bridge is used to shear and drive a flyer disc down a barrel until the flyer disc reaches a maximum velocity Just prior to impacting the explosive (HNS) charge. The flyer disc is normally made from a polyimide resin film or thin sheet. A commercially available resin sold by E.I. du Pont de Nemours & Co., Inc. under the trademark "Kapton" is especially suitable. Upon flyer impact a shock wave of such magnitude is generated that the explosive is detonated.
The single flyer disc provides essentially a point initiation of the HNS charge. The detonation front expands spherically as it travels into the explosive charge. It is a one-shot event thus requiring a maximum current dump to burst the foil bridge to obtain sufficient flyer velocity. The short time and maximum current requires a firing set with an overall low circuit inductance, since a high circuit inductance firing set slows the energy transfer too much. This low circuit inductance requirement makes most standard firing sets used for general exploding-bridgewire initiators unsuitable. Their circuit inductance may be as much as 70-80% too high for reliable exploding foil initiation of insensitive explosives such as HNS.
This invention circumvents the critical energy dump of the single flyer exploding foil concept and the exploding-bridgewire firing-circuit-inductance restraints/limitations by using any standard exploding-bridgewire initiator firing set and the standard bridgewire type detonator construction. Rather than initiating the surrounding explosive directly with the radially exploding-bridgewire as in a conventional exploding-bridgewire device, in this invention the plasma expansion of the exploding-bridgewire is confined and funneled to drive five or more flyers to impact the explosive with sufficient total energy and extended pressure-pulse duration to initiate any explosive, regardless of how insensitive the explosive or explosive mixture is.